Operation management method of iron carbide production process

ABSTRACT

Provided is a method for managing an operation of a producing process for obtaining an iron carbide product having a goal composition in a two-stages reaction process. A first-stage reaction process for partially reducing an iron-containing material for iron making is carried out, and a second-stage reaction process for performing further reduction and carburization is then carried out. A solid sample is taken at an outlet of a reactor for the first-stage reaction process to measure a reduction ratio of the solid sample. By regulating a parameter capable of changing a reduction ratio of the first-stage reaction process, an IC ratio obtained after the second-stage reaction process can be adjusted.

TECHNICAL FIELD

The present invention relates to a method for setting proper processconditions in producing iron carbide suitable for a raw material foriron making and steel making which comprises iron carbide (Fe 3 C) asthe main component, for example, a raw material for steel making whichis used in an electric furnace and the like.

BACKGROUND ART

The production of steel normally comprises the steps of converting ironore to pig iron using a blast furnace, and thereafter converting the pigiron into steel using an open hearth furnace or a converter. Such atraditional method requires large amounts of energy and large-scaleequipment, and has a high cost. Therefore, for a small-scalesteel-making, a method comprising the steps of directly converting ironore into raw materials used in the steel-making furnace, and convertingthe raw material into steel using an electric furnace and the like hasbeen used. With respect to direct steel making process, a directreduction process has been used to convert iron ore into reduced iron.However, the reduced iron produced by the direct reduction process ishighly reactive and reacts with oxygen in the air to generate heat.Therefore, it is necessary to seal the reduced iron with an inert gas,or by some other measures, during transportation and storage of thereduced iron. Accordingly, iron carbide (Fe 3 C) containing acomparatively high iron (Fe) content, which has a low reaction activityand can be easily transported and stored, has recently been used as theiron-containing material for steel making in an electric furnace and thelike.

Furthermore, an iron-making or steel-making material containing ironcarbide as the main component is not only easy to be transported andstored, but also has the advantage that the carbon combined with ironelement can be used as a source of fuel in an iron-making orsteel-making furnace, and can be used as a source to generatemicrobubbles which accelerate the reaction in the steel-making furnace.Therefore, raw materials for iron making or steel making containing ironcarbide as the main component recently have attracted special interest.

According to a conventional method for producing iron carbide,fine-sized iron ore is charged into a fluidized bed reactor or the like,and is caused to react with a gas mixture comprising a reducing gas (e.g., hydrogen gas) and a carburizing gas (e.g., methane gas and the like)at a predetermined temperature. Thus, iron oxides (e. g., hematite (Fe 2O 3 ), magnetite (Fe 3 O 4 ), wustite (FeO)) in iron ore are reduced andcarburized in a single process (which means a process performed bysimultaneously introducing a reducing gas and a carburizing gas to asingle reactor). The prior art in the field of the present invention hasbeen described, for example, in the publication No. 6-501983 of theJapanese translation of International Patent Application(PCT/US91/05198).

The iron carbide producing process can be expressed by the followinggeneral reaction formula.

3Fe 2 O 3 +5H 2 +2CH 4 →2Fe 3 C+9H 2 O

In the single process, however, reducing reaction and carburizingreaction should be taken into consideration together. In addition, areaction gas composition and a reaction gas temperature which aresuitable for each reaction cannot be applied. As a result, a reactiontime (which is required for conversion into iron carbide) becomeslonger. As compared with a conventional method, it takes a longer timeto obtain a constant amount of raw materials for steel making. For thisreason, there is a drawback that an equipment scale should be enlargedto increase the production per unit time.

The present inventors have filed a patent application Japanese PatentApplication No. 8-30985) related to novel technology for a method andapparatus for producing iron carbide which can perform various actionsfor each operation, increase flexibility as a process, shorten areaction time and reduce an amount of a reaction gas to be used. Thisinvention relates to a method for producing iron carbide comprising thesteps of performing a first-stage reaction process for carrying out apart of reducing reaction of iron ore comprising hematite as the maincomponent and then performing a second-stage reaction process forcarrying out further reducing and carburizing reaction and haseliminated all drawbacks of the conventional iron carbide producingmethod and is an epoch-making method for producing iron carbide.

However, also in the case where iron carbide is produced in thetwo-stages reaction process, an iron carbide product having a goalcomposition cannot always be obtained.

The reason is as follows. A lot of reaction parameters such as areaction gas composition, a reaction temperature, a reaction pressureand the like are concerned in generation of the iron carbide. In somecases, the reaction parameters are slightly changed so that undesiredproducts (having a low rate of conversion into iron carbide, forexample) are obtained. If the reaction parameters get out of a constantrange, free carbon is sometimes generated.

There has been proposed a method for controlling quality of an ironcarbide product characterized in that whether a composition of anobtained product can be permitted or not is checked by the Mbssbaueranalysis method in order to control a composition of an iron carbideproduct within a constant range, and the reaction parameters are changedif the composition is not kept within a tolerance. (For example, seeU.S. Pat. No. 5073194, PCT/US91/05188).

However, the Mössbauer analyzer has a drawback that it takes a long time(1 to 4 hours) to perform the measurement in order to enhance theprecision. Accordingly, there has been a problem that it is impossibleto take the proper actions corresponding to conditions in a reactorwhich are changed momently.

In consideration of the above-mentioned problems of the prior art, it isan object of the present invention to provide a method for managing anoperation of a producing process for obtaining an iron carbide producthaving a goal composition in a two-stages reaction process.

DISCLOSURE OF INVENTION

In order to attain the above-mentioned object, the present invention ischaracterized in that a reduction ratio obtained after a first-stagereaction process is changed on the basis of the knowledge that thereduction ratio obtained after the first-stage reaction process and aniron carbide ratio (hereinafter referred to as an IC ratio) obtainedafter a second-stage reaction process has a correlation therebetween,thereby regulating the IC ratio obtained after the second-stage reactionprocess.

The present invention provides a method for managing an operation of aniron carbide producing process, comprising the steps of performing afirst-stage reaction process for partially reducing variousiron-containing materials for iron making, and then performing asecond-stage reaction process for carrying out further reduction andcarburization, is characterized in that a solid sample at an outlet of areactor for the first-stage reaction process is taken to measure areduction ratio of the solid sample, and a parameter capable of changingthe reduction ratio of the first-stage reaction process is regulated toadjust an IC ratio obtained after the second-stage reaction process.

In general, if the reduction ratio of the first-stage reaction processis decreased, a time required for generating iron carbide in thesecond-stage reaction process is increased. On the other hand, if thereduction ratio of the first-stage reaction process is increased, thetime required for generating iron carbide in the second-stage reactionprocess is shortened. More specifically, in the case where apredetermined iron-containing material for iron making is reduced andcarburized in the two-stages reaction process, assuming that a reactiontime is set constant, the IC ratio obtained after the second-stagereaction process is decreased if the reduction ratio of the first-stagereaction process is decreased, and the IC ratio obtained after thesecond-stage reaction process is increased if the reduction ratio of thefirst-stage reaction process is increased. Accordingly, the IC ratioobtained after the second-stage reaction process can be controlled byregulating parameters capable of changing a reduction ratio of thefirst-stage reaction process, that is, a reaction temperature, areaction pressure, a gas composition, a bed height of a fluidized bedand the like, as described above. Examples of a sure method formeasuring a reduction ratio of a solid sample includes a method foranalyzing a composition of a solid. However, X-ray diffraction or thelike takes a long time to perform measurement. Therefore, it ispreferable that a relationship between a magnetic permeability and areduction ratio should be previously obtained and a magneticpermeability should be measured on the basis of the relationship,thereby obtaining a reduction ratio conveniently and rapidly.

Also, the solid sample can be taken between the middle and last chambersof the reactor for the first-stage reaction process in place of thesolid sample at the outlet of the reactor for the first-stage reactionprocess, and the parameter capable of changing the reduction ratio ofthe first-stage reaction process can be regulated corresponding to acorrelation between the reduction ratio of the solid sample and thereduction ratio obtained after the first-stage reaction process, therebyadjusting the IC ratio obtained after the second-stage reaction process.In the case where the inside of a reactor for the first-stage reactionprocess is divided into a lot of chambers, a change in conditions of afed iron-containing material (for example, a change in a preheatingtemperature caused by a fluctuation of water content in iron ore) can bedetected early if a reduction ratio is measured by taking a solid samplebetween the middle and last chambers of the reactor for the first-stagereaction process, as described above. By properly regulating operatingconditions of the reactor for the first-stage reaction process (areaction temperature, a reaction pressure, a bed height of a fluidizedbed and the like) corresponding to a correlation between the reductionratio of the solid sample and the reduction ratio obtained after thefirst-stage reaction process, the reduction ratio obtained after thefirst-stage reaction process can be changed. Consequently, the IC ratioobtained after the second-stage reaction process can be controlled.

Also, the solid sample can be taken between the middle and last chambersof a reactor for the second-stage reaction process in place of the solidsample at the outlet of the reactor for the first-stage reactionprocess, and the parameter capable of changing the IC ratio obtainedafter the second-stage reaction process can be regulated correspondingto a correlation between an IC ratio of the solid sample and the ICratio obtained after the second-stage reaction process, therebyadjusting the IC ratio obtained after the second-stage reaction process.In the case where the inside of a reactor for the second-stage reactionprocess is divided into a lot of chambers, a change in conditions of afed iron-containing material (for example, a change in a preheatingtemperature caused by a fluctuation of water content in iron ore) can bedetected early if an IC ratio is measured by taking a solid samplebetween the middle and last chambers of the reactor for the second-stagereaction process, as described above. By properly regulating operatingconditions of the reactor for the second-stage reaction process (areaction temperature, a reaction pressure, a bed height of a fluidizedbed and the like) corresponding to a correlation between the IC ratio ofthe solid sample and the IC ratio obtained after the second-stagereaction process, the IC ratio obtained after the second-stage reactionprocess can be controlled.

In up-stream chambers to the middle chamber of the reactor (which arecloser to an inlet of the reactor), the reaction does not progressuniformly. Therefore, a fluctuation of a composition of the taken solidsample is great. For this reason, the forward chambers to the middlechamber of the reactor are not suitable for positions in which the solidsample is taken. As described above, it is preferable that the solidsample should be taken between the middle and last chambers of thereactor.

Alternatively, the reduction ratio of the solid sample is not measuredbut an outlet gas composition is measured after mixing at an outlet ofthe reactor and is compared with an inlet gas composition. Thus, adegree of the progress in the reaction of the solid can be decided. So,an exhaust gas sample can be taken for each chamber between the firstand last chambers of the reactor for the first-stage reaction process inplace of the solid sample at the outlet of the reactor for thefirst-stage reaction process, and a gas composition of the reactor forthe first-stage reaction process can be regulated corresponding to acorrelation between the gas composition of the exhaust gas and thereduction ratio obtained after the first-stage reaction process, therebyadjusting the IC ratio obtained after the second-stage reaction process.In the case where the inside of the reactor for the first-stage reactionprocess is divided into a lot of chambers, it is preferable that a gascomposition of each chamber should be measured to perceive a change inthe reaction of each chamber. As described above, a composition of anexhaust gas of each chamber is measured so that the degree of progressin the reaction of the solid can be estimated with high precision andthe abnormalities in the reactor can be detected early. Therefore, thegas composition of the reactor for the first-stage reaction process isappropriately regulated corresponding to a correlation between thecomposition of the exhaust gas and the reduction ratio obtained afterthe first-stage reaction process, thereby changing the reduction ratioobtained after the first-stage reaction process. Consequently, the ICratio obtained after the second-stage reaction process can becontrolled.

Furthermore, an exhaust gas sample can be taken for each chamber betweenthe first and last chambers of a reactor for the second-stage reactionprocess in place of the solid sample at the outlet of the reactor forthe first-stage reaction process, and a gas composition of the reactorfor the second-stage reaction process can be regulated corresponding toa correlation between the gas composition of the exhaust gas and the ICratio obtained after the second-stage reaction process, therebyadjusting the IC ratio obtained after the second-stage reaction process.In the case where the inside of the reactor for the second-stagereaction process is divided into a lot of chambers, a gas composition ofeach chamber can be measured to estimate a degree of progress in thereaction of the solid with high precision and the abnormalities in thereactor can be detected early, as described above. Therefore, the gascomposition of the reactor for the second-stage reaction process isappropriately regulated corresponding to a correlation between thecomposition of the exhaust gas and the IC ratio obtained after thesecond-stage reaction process. Consequently, the IC ratio obtained afterthe second-stage reaction process can be controlled.

According to the present invention having the above-mentionedconstitution, in producing the iron carbide in the fluidized bedreactor, the two-stages reaction process for performing the furtherreducing and carburizing reaction after the partial reducing reactioncan be performed under the proper operating conditions. Therefore, theiron carbide product having a goal composition can be efficientlyproduced.

Also, according to the present invention, in the case where the productcomposition gets out of the range of the goal product composition, theproper operating conditions are selected corresponding to the state inthe fluidized bed reactor so that the operation of the fluidized bedreactor can be easily managed.

Furthermore, in the case where the present invention is applied to arectangular (cross flow) moving bed reactor as well as the fluidized bedreactor, the same effects can be also obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing an example of a schematic structure of anexperimental apparatus for applying a method for producing iron carbideaccording to the present invention;

FIG. 2 is a view showing a schematic structure of an embodiment of anapparatus for producing iron carbide for applying the method forproducing iron carbide according to the present invention; and

FIG. 3 is an enlarged view showing a gas sampling portion of a fluidizedbed reactor.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below withreference to the drawings.

(1) Experimental Apparatus

An example of an experimental apparatus for applying a method forproducing iron carbide according to the present invention comprisesfluidized bed reactor 1 and peripheral apparatus thereof as shown inFIG. 1. Fluidized bed reactor 1 generally has a cylindrical shape andwas provided with electric heater 2 on the outside thereof to set apredetermined temperature. Pipe of 50A (nominal size, outside diameterof 60.5 mm) was used as a principal part of fluidized bed reactor 1. Inaddition, temperature-detecting sensors 3 a, 3 b, 3 c, 3 d, 3 e and 3 fwere positioned along the length of fluidized bed reactor 1 at 127 mm,187 mm, 442 mm, 697 mm and 1707 mm from the bottom of fluidized bedreactor 1, and at the top of fluidized bed reactor 1, respectively, inorder to measure the temperature of the inside of fluidized bed reactor1.

Hopper 4 was connected to the upper portion of fluidized bed reactor 1by line 7 via lock hopper 6 having valve 5 provided in the front and inthe rear. Consequently, a fine-sized feed (for example, an iron orematerial comprising hematite (Fe 2 O 3 ) as the main component) could becaused to flow from hopper 4 into fluidized bed reactor 1 in apressurized state. In addition, line 9 having cooler 8 attached theretowas connected to the bottom of fluidized bed reactor 1 to cool anddischarge the feed (raw material) in fluidized bed reactor 1.

The bottom of fluidized bed reactor 1 was connected to gas holder 10 vialines 11 and 12 to allow a flow of a reaction gas having a predeterminedcomposition in gas holder 10 into fluidized bed reactor 1. Further,saturator 13 was provided between lines 11 and 12 to saturate thereaction gas with water.

Lines 14, 15 and 16 were connected in series to the upper portion offluidized bed reactor 1 to direct an exhaust gas obtained after reactionto an incinerator apparatus (not shown). In addition, a dust of the feedcontained in the exhaust gas was removed by dust collector 17 providedbetween lines 14 and 15 and filter 18 installed on line 15. The exhaustgas was cooled by gas cooler 19 installed on line 15 to condense water.The condensed water could be separated by drain separator 19 a.

(2) Experimental Conditions and Results

An experiment for converting iron ore mainly containing hematite (Fe 2 O3 ) into iron carbide, that is, an experiment according to the presentinvention which is divided into partial reducing reaction and furtherreducing and carburizing reactions was carried out by performing aprocess for subjecting the iron ore to the first-stage reaction processusing a reducing gas mainly comprising hydrogen, and then performing aprocess for subjecting the iron ore to the second-stage reaction processusing a gas mixture containing a reducing gas and a carburizing gasmainly comprising hydrogen and methane. The iron ore had a compositionof 97.3% by weight of Fe 2 O 3 , 1.4% by weight of FeO, and 1.3% byweight of Fe, and had a particle size of 1.0 mm or less 3.52 kg of theiron ore was supplied into fluidized bed reactor 1. The inside offluidized bed reactor 1 had a pressure of 3 to 4 kgf/cm² G (Grepresenting a gauge pressure), and had a temperature of 590 to 650° C.The compositions of the feed (raw material iron ore) and the reactiongas are changed as set forth in the following Table 1. In Table 1,(outlet side-inlet side) indicating the change in the reaction gascomposition represents subtract (a mean value on the inlet side offluidized bed reactor 1 during the period) from (a mean value on theoutlet side of fluidized bed reactor 1 during the period) which aremeasured by the on-line gas chromatography method. That is to say,

outlet side=a mean value on the outlet side of fluidized bed reactor 1during the period;

inlet side=a mean value on the inlet side of fluidized bed reactor 1during the period.

In Table 1, an initial stage means the first-stage reaction process, andmiddle and latter stages mean the second-stage reaction process.

TABLE 1 Inital stage Middle stage Latter stage 0 0.5 hr 1.25 hr 2.25 hr5.25 hr 6.25 hr Composition of Raw Material and Product Fe₂O₃ 97.3   0.2 1.4  0.6 0.0 0.0 Fe₃O₄ 0.0 59.2 18.8 13.0 5.8 5.1 FeO 1.4 29.5 34.719.6 2.6 1.7 Fe 1.3 11.1 45.1 22.6 0.0 0.0 Fe₃C 0.0  0.0  0.0 44.2 91.6 93.2  (Outlet side- (Outlet side- (Outlet side- Inlet side) Inlet side)Inlet side) Reaction Gas Composition A 268 Nm³/hr CH₄ +1.8 −0.3 −3.1 H₂−9.9 −4.3 +2.9 H₂O +9.1 +4.3 +3.0 Reaction Gas Composition B 90 Nm³/hrCH₄ +1.1 −4.8 −2.0 H₂ −11.5  −1.8 +1.1 H₂O +0.9 +6.7 +3.1

As is clearly shown in Table 1, the feed is partially reduced in thefirst-stage reaction process, and the further reduction andcarburization are performed in the second-stage reaction process. Ittakes about 6.25 hours to obtain a conversion ratio of 93% or more whichis suitable for an iron carbide product. More specifically, in the casethat the feed (raw material) shown in Table 1 is subjected to thefirst-stage reaction process by using a reducing gas mainly comprisinghydrogen and to the second-stage reaction process by using a gas mixturecontaining a reducing gas and a carburizing gas mainly comprisinghydrogen and methane at a pressure of 3 to 4 kgf/cm² G and a temperatureof 590 to 650° C., it is predicted that an iron carbide product having aconversion ratio of 93.2% into iron carbide can be obtained when 6.25hours pass after the reaction begins (which will be hereinafter referredto as batch reaction data).

In the case where operating conditions such as a supply amount of theraw material, a composition of the raw material, a composition of areaction gas, a flow rate of the reaction gas, a reaction pressure, areaction temperature and the like are set to predetermined values in aspecific fluidized bed reactor, a residence time distribution in eachchamber in the reactor has a constant value. By executing a lot ofexperiments, it is possible to previously grasp a state of transferunder predetermined operating conditions of a specific fluidized bed.The residence time distribution means the following. In the fluidizedbed reactor having a lot of chambers, the raw material in each chambercomprises a combination of various different residence-in-reactor times.The combination becomes constant if the operating conditions aredetermined. For example, if 25% of the raw material in some chamber hasa residence-in-reactor time of 1 to 1.5 hours, 50% of the raw materialhas a residence-in-reactor time of 1.5 to 2 hours and 25% of the rawmaterial has a residence-in-reactor time of 2 to 2.5 hours, thiscombination is referred to as the residence time distribution.Accordingly, if the above-mentioned batch reaction data are obtained bypreviously executing experiments for various kinds of iron orematerials, it is possible to predict a composition of an outlet sideproduct when an iron ore material having a certain composition ischarged into the fluidized bed reactor having a known transfer state asa product sum of the residence time distribution and the batch reactiondata in the specific fluidized bed reactor. By selecting the operatingconditions of the first-stage reaction process and the second-stagereaction process so that a predicted composition of the outlet sideproduct is kept within the range of a goal product composition, it ispossible to obtain an iron carbide product having goal quality.

When the range of the goal quality should be changed or the goal qualitygets out of the same range, it is possible to control the quality bycorrecting the operating conditions (the supply amount of the rawmaterial, the composition of the raw material, the composition of thereaction gas, the flow rate of the reaction gas, the reaction pressure,the reaction temperature and the like). Taking it into considerationthat a state value which can be detected in a sufficiently short timefor a response time under the operating conditions, and has a great gainfor correction and a high astringency is effective in control of thequality under the operating conditions, the present inventors have founda method. An example of the method will be described below.

As a method for measuring a reduction ratio of a solid sample, a methodfor estimating the reduction ratio by measuring a magnetic permeabilityis preferable because it can be performed conveniently and rapidly. Morespecifically, if a relationship between the composition and the magneticpermeability of the iron carbide product is obtained in advance,effective countermeasures can be taken by using the relationship as atest curve. For example, the magnetic permeability of the solid sampleat an outlet of the reactor for the first-stage reaction process or froma middle position to the outlet of the reactor for the first-stagereaction process is measured (in order to control a degree of partialreduction of the outlet side product at the outlet of the reactor forthe first-stage reaction process), or the magnetic permeability of thesolid sample at an outlet of the reactor for the second-stage reactionprocess or from a middle position to the outlet of the reactor for thesecond-stage reaction process is measured (in order to control quality(IC ratio) of the product obtained after the second-stage reactionprocess). If the magnetic permeability gets out of a preferable range onthe test curve, the reaction gas composition or the reaction temperatureis changed in the following manner. Consequently, it is possible toobtain an iron carbide product having a goal composition.

By adding methane to the reducing gas in the first-stage reactionprocess, a composition ratio of hydrogen can be changed. Consequently,it is possible to control the reaction time required for obtaining thereduction ratio in the first-stage reaction process and a predeterminedreduction ratio. By adding hydrogen or methane to the reducing gas andthe carburizing gas in the second-stage reaction process, a compositionratio of hydrogen to methane can be changed. Consequently, it ispossible to control the reaction time required for obtaining acarburization ratio (conversion ratio into iron carbide) in thesecond-stage reaction process and a predetermined carburization ratio.In this case, if a sample is obtained in the middle position of thereactor in each reaction process, a variation in the magneticpermeability is great and an operating state can be grasped clearly. Byearly detecting the quality at the outlet of the reactor, it can beexpected that effects of the quality control are increased. Furthermore,it is possible to control the carburization ratio of a final product,and the form and amount of residual iron oxide by performing theabove-mentioned reaction processes.

It is preferable that the reaction temperature in the first-stagereaction process should be set to 550 to 750° C. If the reactiontemperature is lower than 550° C., the reaction speed is low and thereaction time is increased. If the reaction temperature is higher than750° C., it brings a problem to a heat resistant structure of thereactor. There is a possibility that the reducing reaction of hematitemight cause sintering within the range of about 600° C. to about 700° C.and the reaction time might be increased. For this reason, the reactionhas conventionally been performed at a temperature of about 590° C.which is lower than the above temperature range. According to thepresent invention, the reducing reaction is divided into two steps, andthe reduction ratio in the first-stage reaction process is not increasedgreatly. Therefore, even if the reaction temperature is increased, thesintering is not caused and the reaction speed is not decreased.

The second-stage reaction process performs further reduction andcarburization at the same time. The sintering is caused with moredifficulty than in the case where only the reduction is carried out.Therefore, it is preferable that the reaction temperature should be seta little higher, that is, to about 610 to 750° C. in order to shortenthe reaction process time. It is sometimes desirable that portions otherthan iron carbide in the iron carbide product should comprise Fe 3 O 4which is most stable. In that case, the reaction can be performed bysetting a temperature of about 575° C. or less where a little unstableFeO is not present, for example, by setting the temperature of thesecond-stage reaction process to about 550 to 570° C., and residual ironcan contain only Fe 3 O 4.

As expressed by the general reaction formula, it is supposed that anamount of H 2 O in the reaction gas is increased if the reducingreaction and the carburizing reaction progress. If a change in theamount of H 2 O in the reaction gas is known, a degree of the progressin the reaction can be detected. If the amount of H 2 O in the reactiongas is measured by the on-line gas chromatography method, for example,various actions can be taken to detect the degree of the progress in thereaction by an H 2 O value and to control the progress in the reaction.

In some cases, the reaction progresses more quickly or slowly than inTable 1 depending on the kind of iron ore as set forth in the followingTable 2. In Table 2, “reaction progresses quickly” means the case wherea composition obtained after 1.25 hours in Table 1 was set to an initialvalue and a reaction for 2 hours was completed in one hour, and“reaction progresses slowly” means the case where the compositionobtained after 1.25 hours in Table 1 was set to an initial value and thereaction for 0.5 hour required 1 hour.

TABLE 2 Reaction Progresses Quickly Reaction Progresses Slowly EarlyStage of Reaction Early Stage of Reaction Composition of Raw Materialand Product Fe₂O₃ 1.4 → 0.0 1.4 → 1.0 Fe₃O₄ 18.8 → 10.3 18.8 → 14.9 FeO34.7 → 10.6 34.7 → 26.3 Fe 45.1 → 0.0  45.1 → 35.7 Fe₃C  0.0 → 79.1  0.0→ 22.1 (Outlet side - Inlet Side) (Outlet side - Inlet Side) ReactionGas Composition C 268 Nm³/hr CH₄ −4.8 −3.6 H₂ −0.3 −0.2 H₂O +5.0 +3.8Reaction Gas Composition D 90 Nm³/hr CH₄ −8.1 −4.9 H₂ +0.6 +0.2 H₂O +9.1+5.1

Table 2 can also be utilized for detecting the degree of the progress inthe reaction in the same manner as Table 1.

(3) Summary of Producing Apparatus

FIG. 2 is a view showing a schematic structure of an iron carbideproducing apparatus suitable for applying the method for producing ironcarbide according to the present invention. The producing apparatuscomprises first-stage reaction process portion 20 for performing partialreducing reaction of an iron-containing material for iron making, andsecond-stage reaction process portion 40 for performing further reducingreaction and carburizing reaction. First-stage reaction process portion20 includes lines 21 and 22, compressor 23, line 24, heat exchanger 25,line 26, heater 27, line 28, fluidized bed reactor 29, line 30, heatexchanger 25, line 31, scrubber 32 and line 33 which form a loop. Areaction gas is supplied to a bottom gas inlet of fluidized bed reactor29 through line 22, compressor 23, line 24, heat exchanger 25, line 26,heater 27 and line 28, and flows from a top gas outlet of fluidized bedreactor 29 to line 30, heat exchanger 25, line 31, scrubber 32, line 33,line 21 and line 22 in order. Thus, a loop for causing a first reactiongas to circulate is formed. Although a pressure is dropped while the gascirculates in each device, the pressure is raised properly by compressor23 so that the reaction gas can circulate in the loop. The reaction gasflowing into fluidized bed reactor 29 exchanges heat with a reacted gasflowing out of reactor 29 by heat exchanger 25, and is further heated byheater 27 to a suitable reaction temperature. Scrubber 32 compriseshollow body 34, line 35 for jetting water into the gas, and line 36 fordischarging water in body 34, and serves to cool the gas flowing out ofreactor 29, and condenses and removes steam in the gas. Furthermore, agas having a predetermined composition is supplied to a circulation paththrough line 37 connected to a portion where lines 21 and 22 are coupledto each other. In addition, a predetermined amount of the gas can beexhausted from the circulation path via line 38 connected to a portionwhere lines 33 and 21 are coupled to each other. By regulating thequantity of the supply gas and the exhaust gas, the composition of thereaction gas flowing into reactor 29 is fixed and a change in the gascomposition and a decrease in the reaction speed by the reaction can beprevented from being caused.

A flow of the reaction gas in second-stage reaction process portion 40is also the same as in first-stage reaction process portion 20.Therefore, common portions are indicated at reference numerals having 20attached to the reference numerals of first-stage reaction processportion 20, and description will be omitted.

A flow of the feed (raw material) into the reactors is as followsFine-sized iron ore is steadily supplied into an upper portion offluidized bed reactor 29 of first-stage reaction process portion 20thereinto through line 60. The fine-sized iron ore which has completelybeen subjected to the partial reducing reaction is continuously suppliedfrom a lower portion of fluidized bed reactor 29 to fluidized bedreactor 49of second-stage reaction process portion 40 through line 61.Further reducing reaction and carburizing reaction are performed influidized bed reactor 49, and the converted iron carbide is continuouslydischarged through line 62.

It is sufficient that only reducing reaction is taken into considerationfor the first-stage reaction process as the composition of the reactiongas used in each process. Therefore, the first-stage reaction process isperformed by using the reducing gas mainly comprising hydrogen. For thisreason, a hydrogen concentration and a reaction speed of the reducingreaction can be increased, and the reaction time can be shortened morethan in the prior art. Since the reducing reaction and the carburizingreaction should be taken into consideration for the second-stagereaction process, a gas mixture containing hydrogen and methane is used.However, the reducing reaction partially progresses in the first-stagereaction process. Therefore, importance can be attached to thecarburizing reaction. Accordingly, a methane concentration can be raisedto increase the speed of the carburizing reaction and to shorten thereaction time. A constant amount of methane can be added to the reducinggas mainly comprising hydrogen in the first-stage reaction process todecrease the hydrogen concentration and to control the speed of thereducing reaction. By regulating the methane concentration of thereaction gas in the second-stage reaction process, the speed of thecarburizing reaction can be controlled, deposition of free carbon can bedecreased and the reaction time to obtain a predetermined carburizationratio can be controlled.

FIG. 3 is an enlarged view showing a gas sampling portion of a fluidizedbed reactor. In FIG. 3, suction portion 71 is fixed in a lower positionthan top 74 of partition wall 73 of the fluidized bed reactor diagonallywith respect to sidewall 72 of the fluidized bed reactor. It ispreferable that a gradient (angle θ) of suction pipe 75 for insertioninto suction portion 71 should be sufficiently greater than an angle ofrepose of the feed (raw material). It is preferable that a lot of airshould not be sucked and that a flow velocity should be set without fineparticles having a size of 10μ or more. Preferably, a distance L betweenvalve 76 attached to suction pipe 75 and suction portion 71 iscomparatively increased and a temperature of valve 76 is decreased byradiation of heat therebetween. Filter 78 made of glass wool is attachedto the inside of dust separator 77 installed on a rear face of valve 76,thereby removing a dust. Valve 79 is fixed to a bottom of dust separator77, and dust pot 80 is provided. It is preferable that the gas should bedischarged in an amount of about 100 milliliter/min. from valve 81installed on a top of dust separator 77. In order to prevent generationof drain, it is preferable that dust separator 77, other accessoryvalves and the like should be put in a thermostatic box.

By using a gas sampling apparatus having the above-mentioned structure,an exhaust gas sample is taken for each chamber from the inlet to thelast chamber of the outlet in the reactor for the first-stage reactionprocess (in order to control the degree of the partial reduction of theoutlet side product at the outlet in the reactor for the first-stagereaction process), or an exhaust gas sample is taken for each chamberfrom the inlet to the last chamber of the outlet in the reactor for thesecond-stage reaction process (in order to control the quality (ICratio) of the product obtained after the second-stage reaction process)to measure these gas compositions by the gas chromatography method orthe like. If the gas composition gets out of the preferable range, thequality (IC ratio) of the product can be controlled by changing the gascompositions in the first-stage reaction process and the second-stagereaction process as described above.

INDUSTRIAL APPLICABILITY

Since the present invention has the above-mentioned constitution, thepresent invention is suitable to an apparatus for obtaining an ironcarbide product having a goal composition in a two-stages reactionprocess.

What is claimed is:
 1. A method of managing an operation of an ironcarbide producing process, comprising steps of: performing a first-stagereaction process for partially reducing various iron-containingmaterials for iron making, and then performing a second-stage reactionprocess for carrying out further reduction and carburization; taking asolid sample at an outlet of a reactor for the first-stage reactionprocess to measure a magnetic permeability of the solid sample;obtaining a reduction ratio of the solid sample from the magneticpermeability as measured using a relationship between the compositionand the magnetic permeability of the iron carbide product, which wasobtained in advance; and regulating a parameter capable of changing thereduction ratio of the first-stage reaction process to adjust an ironcarbide ratio obtained after the second-stage reaction process using arelationship that assuming a reaction time is set constant the ironcarbide ratio obtained after the second-stage reaction process isdecreased if the reduction ratio of the first-stage reaction process isdecreased and the iron carbide ratio obtained after the second-stagereaction process is increased if the reduction ratio of the first-stagereaction process is increased.
 2. The method of managing an operation ofan iron carbide producing process according to claim 1, wherein thesolid sample is taken between the middle and end of the reactor for thefirst-stage reaction process in place of the solid sample at the outletof the reactor for the first-stage reaction process to measure amagnetic permeability of the solid sample; obtaining a reduction ratioof the solid sample from the magnetic permeability as measured using arelationship between the composition and the magnetic permeability ofthe iron carbide product, which was obtained in advance; and theparameter capable of changing the reduction ratio of the first-stagereaction process is regulated corresponding to a correlation between thereduction ratio of the solid sample and the reduction ratio obtainedafter the first-stage reaction process; thereby adjusting iron carbideratio obtained after the second-stage reaction process.